We propose to optimize non-primate Feline Immunodeficiency Virus (FIV) vectors for the treatment of hemophilia A to address the need for constitutive, long-term expression of the therapeutic protein, factor VIII. Lentiviral vectors offer multiple advantages over other gene delivery vehicles for gene therapy and FIV has particular advantages over other lentiviral vectors. Importantly, FIV is non-pathogenic in humans. FIV vectors have been shown to efficiently express transgenes in a variety of tissues and species, including primates. The long-term objective is to develop a commercially feasible FIV vector system. For that purpose, we propose to optimize the FIV vector technology in vitro and in vivo to increase the overall efficiency of this gene delivery system. The specific goals are to generate the next generation FIV-based vectors optimized for safety, high titer and efficacy for delivery of human FVIII and to evaluate the in vivo efficacy of the optimized FIVIFVIII vectors in mouse models for hemophilia A. The combined optimization of the FIV vector system itself in vitro and the identification of the best mode delivery in vivo are expected to increase the overall potency of FIV vectors for hemophilia A. Increased vector potency translates into lower doses and thus fewer risks. PROPOSED COMMERCIAL APPLICATION: NOT AVAILABLE